Method

Step 1

Bring the water and clam juice to a boil over high heat in a large soup pot with the scallion whites, lemongrass, ginger, garlic, and chili paste. Cover and adjust the heat to maintain a simmer, and cook for 10 minutes. Add the fish sauce.

Step 2

Slice the fish into large chunks and add to the broth with the mushrooms and carrots. Cook over medium heat, uncovered, until the fish is opaque and cooked through, about 4 minutes. (Remove and discard lemongrass.) Stir in the cilantro and scallion greens and season with salt. Spoon into warm bowls and serve with lime wedges.